It sounds like you're getting mixed up between two different uses of "pelvic tilt". In the context of the article you linked, "pelvic tilt" refers to rotation (movement) of the pelvis in space, while the femurs are fixed in position. This is what is supposed occur in the movement of a Romanian deadlift - the legs remain still while the pelvis (and torso) rotates forward to lower the weight, and then rotates backward to raise the weight back up. In the context of the dubious postural diagnosis of "anterior pelvic tilt", "pelvic tilt" refers to the position of the pelvis rather than a movement, and describes a pelvis which normally sits tilted forward relative to the torso.
If we squeeze our glutes as much as possible, we will perform simultaneously both hips extension and posterior pelvic tilt, or do them depend also on other factors?
If the hips are fixed in position, like in a leg press, then hip extension will be achieved by rotation of the femurs. If the femurs are fixed in position, like in a Romanian deadlift, then hip extension will be achieved by rotation of the pelvis.
If hips extension means a simultaneous force that tries to posteriorly tilt the pelvis, should we focus on counteracting it with our lumbar extensors while extending the spine?
It's not "counteracting" the glutes, but in "posterior chain" exercises like squats, deadlifts, and RDLs it's typical for the glutes and spinal extensors to act together, with the spinal extensors holding the spine in position relative to the pelvis while the hip extensors (including the glutes) rotate the pelvis and torso together.
